There has heretofore been known a drive apparatus of a vehicle including a differential mechanism through which an output of a drive power source, such as an engine or the like, is distributed to a first electric motor and an output member, and a second electric motor disposed between the output member and drive wheels. Such drive apparatus for a hybrid vehicle is disclosed for example in Patent Publication 1. The drive apparatus includes a differential mechanism being comprised of a planetary gear unit i.e., gear set and performing as the differential action for mechanically transmitting a major part of power outputted from the engine to drive wheels. A remaining part of power from the engine is electrically transmitted from the first electric motor to the second electric motor using an electrical path.
Thus, the drive apparatus operates as a transmission of which shifting ratio i.e., gear ratio is electrically changed, for example as an electrically controlled continuously variable automatic transmission. The drive apparatus is controlled by the control device so that the vehicle runs i.e., is driven with the optimum operation state of the engine, thus improving fuel consumption, i.e., mileage.
Patent Publication 1: JP 2003-301731
In general, the continuously variable transmission has heretofore been known as a device for improving fuel consumption of a vehicle. A gear type power transmitting device such as a step variable automatic transmission has heretofore been known as a device having high transmitting efficiency. However, no power transmitting mechanism having such combined advantages has been put into practical use yet. For instance, the hybrid vehicle drive apparatus, disclosed in the above Patent Publication 1, includes the electrical path through which electric energy is transmitted from the first electric motor to the second electric motor, that is, a transmitting path through which a part of the vehicle drive force is transmitted in the form of electric energy. This inevitably causes the first electric motor to be made large-size with an increase in an output of the engine. Also, the second electric motor, driven with electric energy output from the first electric motor, is caused to increase in size. Thus, an issue arises with the occurrence of an increase in size of the drive apparatus.
Alternately, the part of the engine output is transmitted to the driving wheel after converted to the electric energy once, which may worsen the mileage depending on the vehicle running condition such as the high speed running i.e., driving. Similar problem may occur when the above power distributing mechanism is used as the continuously variable machine called the electrically controlled CVT in which the shifting ratio is electrically changed.
With the drive apparatus for hybrid vehicle disclosed in Patent Publication 1, further, there has heretofore been known a transmission incorporated in a power transmitting path between an output member of a differential mechanism (electrically controlled continuously variable shifting portion) and drive wheels with a view to minimizing a required capacity of the second electric motor to meet a need for increasing drive torque. With such a drive apparatus for vehicle, an output of a drive power source is transferred to the drive wheels via two shifting mechanisms including the electrically controlled continuously variable shifting portion and the transmission, while permitting the drive apparatus to establish a total gear ratio based on respective gear ratios of the shifting mechanisms.
When this takes place, if the transmission executes the shifting, then, a need arises to execute the control of the continuously variable shifting portion with such a shifting. This causes likelihood of the transmission and the continuously variable shifting portion complicated in control, unlike the transmission and the continuously variable shifting portion are provided independently for respective controls, resulting in the occurrence of shifting shocks.
As one example of the transmission, a step variable automatic transmission (hereinafter referred to as “step variable transmission”) has been known including an engaging device for selectively engaging plural sets of rotary elements of a planetary gear set to be alternatively switched to plural gear positions such as a forward 4th-gear, a forward 5th-gear and a forward 6th-gear, etc. With such a step variable transmission, an engaging pressure of the engaging device is controlled during a shifting so as to suppress the shifting shocks. However, the engaging pressure of the engaging device needs to be controlled in conjunction with a control of the continuously variable shifting portion during the shifting of the step variable transmission. Accordingly, there has been likelihood of the transmission and the continuously variable shifting portion more complicated in control than that independently executed by the step variable transmission, resulting in the occurrence of shifting shocks.
The present invention has been completed with the above view in mind and has an object to provide a control device for vehicle drive apparatus, having a differential mechanism operative to perform a differential action for distributing an output of an engine to a first electric motor and an output shaft, and an electric motor disposed in a power transmitting path between the differential mechanism and drive wheels, which enables the miniaturization of the drive apparatus and/or the improvement in fuel consumption with a capability of suppressing shifting shocks.